301 research outputs found
Water vapor diffusion in Mars subsurface environments
The diffusion coefficient of water vapor in unconsolidated porous media is measured
for various soil simulants at Mars-like pressures and subzero temperatures.
An experimental chamber which simultaneously reproduces a low-pressure,
low-temperature, and low-humidity environment is used to monitor water flux from an ice
source through a porous diffusion barrier. Experiments are performed on four types of
simulants: 40–70 µm glass beads, sintered glass filter disks, 1–3 µm dust (both loose and
packed), and JSC Mars–1. A theoretical framework is presented that applies to
environments that are not necessarily isothermal or isobaric. For most of our samples, we
find diffusion coefficients in the range of 2.8 to 5.4 cm^2 s^-1 at 600 Pascal and 260 K. This
range becomes 1.9–4.7 cm^2 s^-1 when extrapolated to a Mars-like temperature of 200 K.
Our preferred value for JSC Mars–1 at 600 Pa and 200 K is 3.7 ± 0.5 cm^2 s^-1. The
tortuosities of the glass beads is about 1.8. Packed dust displays a lower mean diffusion
coefficient of 0.38 ± 0.26 cm^2 s^-1, which can be attributed to transition to the Knudsen
regime where molecular collisions with the pore walls dominate. Values for the diffusion
coefficient and the variation of the diffusion coefficient with pressure are well matched by
existing models. The survival of shallow subsurface ice on Mars and the providence of
diffusion barriers are considered in light of these measurements
The Globular Cluster System of the Virgo Dwarf Elliptical Galaxy VCC 1087
We have analysed the globular cluster (GC) system of the nucleated dwarf
elliptical galaxy VCC 1087 in the Virgo cluster, based on Keck/LRIS
spectroscopy and archival HST/ACS imaging. We estimate VCC 1087 hosts a total
population of 77+/-19 GCs, which corresponds to a relatively high V-band
specific frequency of 5.8+/-1.4. The g-z color distribution of the GCs shows a
blue (metal-poor) peak with a tail of redder (metal-rich) clusters similar in
color to those seen in luminous ellipticals. Spectroscopy of a subsample of 12
GCs suggests that the GC system is old and coeval (~10 Gyr), with a fairly
broad metallicity distribution (-1.8<[m/H]<-0.8). In contrast, an integrated
spectrum of the underlying galaxy starlight reveals that its optical luminosity
is dominated by metal-rich, intermediate-aged stars. Radial velocities of the
GCs suggest rotation close to the major axis of the galaxy, and this rotation
is dynamically significant with (v/sigma)^* >1. A compilation of the kinematics
of the GC systems of 9 early-type galaxies shows surprising diversity in the
v/sigma parameter for GC systems. In this context, the GC system of VCC 1087
exhibits the most significant rotation to velocity dispersion signature.
Modeling the velocity dispersion profile of the GCs and galaxy stars suggest
fairly constant mass-to-light ratios of ~3 out to 6.5 kpc. The present
observations can entertain both baryonic and non-baryonic solutions, and GC
velocities at larger radii would be most valuable with regard to this issue. We
discuss the evolution of VCC 1087 in terms of the galaxy ``harassment''
scenario, and conclude that this galaxy may well be the remains of a faded,
tidally perturbed Sc spiral [abridged].Comment: 17 pages, 13 figures, to appear in the A
Metabolic crosstalk: molecular links between glycogen and lipid metabolism in obesity.
Glycogen and lipids are major storage forms of energy that are tightly regulated by hormones and metabolic signals. We demonstrate that feeding mice a high-fat diet (HFD) increases hepatic glycogen due to increased expression of the glycogenic scaffolding protein PTG/R5. PTG promoter activity was increased and glycogen levels were augmented in mice and cells after activation of the mechanistic target of rapamycin complex 1 (mTORC1) and its downstream target SREBP1. Deletion of the PTG gene in mice prevented HFD-induced hepatic glycogen accumulation. Of note, PTG deletion also blocked hepatic steatosis in HFD-fed mice and reduced the expression of numerous lipogenic genes. Additionally, PTG deletion reduced fasting glucose and insulin levels in obese mice while improving insulin sensitivity, a result of reduced hepatic glucose output. This metabolic crosstalk was due to decreased mTORC1 and SREBP activity in PTG knockout mice or knockdown cells, suggesting a positive feedback loop in which once accumulated, glycogen stimulates the mTORC1/SREBP1 pathway to shift energy storage to lipogenesis. Together, these data reveal a previously unappreciated broad role for glycogen in the control of energy homeostasis
Keck Spectroscopy of Globular Clusters in the Sombrero Galaxy
We analyze high signal-to-noise spectra for 14 globular clusters (GCs) in the
Sombrero galaxy, NGC 4594 = M104, obtained with the LRIS spectrograph on the
Keck I telescope. We find generally good agreement between spectroscopic
metallicities and previous photometric metallicities based on V-I colors.
Further, we use measurements of various Balmer line indices on co-added spectra
of metal-poor and metal-rich GCs to estimate ages for the GC subpopulations and
find ages of 10-15 Gyr, with preferred ages around 11-12 Gyr and no detectable
differences between the metal-rich and metal-poor subpopulations. However,
because of model and measurement uncertainties, age differences of a few (2-3)
Gyrs cannot be be ruled out. We also measure alpha-to-iron abundance ratios
from Mg and TiO features and find enhancements on the order of +0.4 dex
relative to the Sun, similar to the alpha/Fe abundance ratios observed in other
old stellar populations. Finally, we combined our sample with radial velocities
for 34 GCs from Bridges et al. 1997 and obtain virial and projected masses for
the Sombrero of M(Vir) = 8.1+/-1.8 x 10^11 M(sun) and M(P) = 5.3+/-1.0 x 10^11
Msun within 17 kpc, respectively. Using 12 clusters within the central 4.5 kpc,
the corresponding numbers are M(Vir) = 2.1+/-1.1 x 10^11 Msun and M(P) =
2.0+/-1.3 x 10^11 Msun.Comment: 24 pages, including 9 figures and 3 tables. Accepted for publication
in A
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Factors Influencing Sleep Difficulty and Sleep Quantity in the Citizen Pscientist Psoriatic Cohort.
IntroductionSleep is essential for overall health and well-being, yet more than one-third of adults report inadequate sleep. The prevalence is higher among people with psoriasis, with up to 85.4% of the psoriatic population reporting sleep disruption. Poor sleep among psoriasis patients is particularly concerning because psoriasis is independently associated with many of the same comorbidities as sleep dysfunction, including cardiovascular disease, obesity, and depression. Given the high prevalence and serious consequences of disordered sleep in psoriasis, it is vital to understand the nature of sleep disturbance in this population. This study was designed to help meet this need by using survey data from Citizen Pscientist, an online patient portal developed by the National Psoriasis Foundation.MethodsOur analysis included 3118 participants who identified as having a diagnosis by a physician of psoriasis alone or psoriasis with psoriatic arthritis. Demographic information, psoriasis severity and duration, sleep apnea status, smoking and alcohol consumption, itch timing, and sleep characteristics were included. Two separate multivariate logistic regression models in STATA were used to determine whether the presence of psoriatic arthritis, age, gender, body mass index, comorbid sleep apnea, psoriasis severity, timing of worst itch, smoking status, or high-risk alcohol consumption were associated with sleep difficulty or low sleep quantity, defined by the American Academy of Sleep Medicine as less than 7 h of sleep per night on average.ResultsResults from the multivariate logistic regressions found that sleep difficulty was associated with psoriatic arthritis (OR 2.15, 95% CI [1.79-2.58]), female gender (2.03 [1.67-2.46]), obese body mass index (BMI ≥ 30) (1.25 [1.00-1.56]), sleep apnea (1.41 [1.07-1.86]), psoriasis severity of moderate (1.59 [1.30-1.94]) or severe (2.40 [1.87-3.08]), and smoking (1.60 [1.26-2.02]). Low sleep quantity was associated with obese BMI (1.62 [1.29-2.03]), sleep apnea (1.30 [1.01-1.68]), psoriasis severity of moderate (1.41 [1.16-1.72]) or severe (1.40 [1.11-1.76]), and smoking (1.62 [1.31-2.00]). Sleep difficulty and low sleep quantity were not associated with age, alcohol consumption, or timing of worst itch.ConclusionThese results are potentially meaningful in several aspects. We identify an important distinction between sleep difficulty and sleep quantity in psoriatic disease, whereby having psoriatic arthritis and being female are each associated with sleep difficulty despite no association with low sleep quantity. Furthermore, there is conflicting evidence from prior studies as to whether psoriasis severity is associated with sleep difficulty, but this well-powered, large study revealed a strong, graded relationship between psoriasis severity and both sleep difficulty and low sleep quantity. Overall, our results show that both sleep difficulty and low sleep quantity were associated with multiple factors in this analysis of a large psoriatic cohort. These findings suggest that dermatologists may gather clinically useful information by screening psoriatic patients for trouble sleeping and low sleep quantity to identify potential comorbidities and to more effectively guide disease management
Dynamical Constraints on the Formation of NGC 4472 and Its Globular Clusters
We present new radial velocities for 87 globular clusters around the
elliptical galaxy NGC 4472, and combine these with our previously published
data to create a data set of velocities for 144 globular clusters around NGC
4472. We utilize this data set to analyze the kinematics of the NGC 4472
globular cluster system. The new data confirms our previous discovery that the
metal-poor clusters have significantly higher velocity dispersion than the
metal-rich clusters in NGC 4472. We also find very little or no rotation in the
more spatially concentrated metal-rich population, with a resulting upper limit
for this population of (v/sigma)_{proj} < 0.34 at a 99% confidence level. The
very small angular momentum in the metal-rich population requires efficient
angular momentum transport during the formation of this population which is
spatially concentrated and chemically enriched. Such angular momentum transfer
can be provided by galaxy mergers, but has not been achieved in other extant
models of elliptical galaxy formation that include dark matter halos. We also
calculate the velocity dispersion as a function of radius, and show that it is
consistent with roughly isotropic orbits for the clusters and the mass
distribution of NGC 4472 inferred from X-ray observations of the hot gas around
the galaxy.Comment: Accepted for publication in the Astronomical Journal, 27 pages, 4
figure
DEER Spectroscopy Measurements Reveal Multiple Conformations of HIV-1 SOSIP Envelopes that Show Similarities with Envelopes on Native Virions
HIV-1 Envelope (Env) mediates viral-host membrane fusion after binding host-receptor CD4 and coreceptor. Soluble envelopes (SOSIPs), designed to mimic prefusion conformational states of virion-bound envelopes, are proposed immunogens for eliciting neutralizing antibodies, yet only static structures are available. To evaluate conformational landscapes of ligand-free, CD4-bound, inhibitor-bound, and antibody-bound SOSIPs, we measured inter-subunit distances throughout spin-labeled SOSIPs using double electron-electron resonance (DEER) spectroscopy and compared results to soluble and virion-bound Env structures, and single-molecule fluorescence resonance energy transfer (smFRET)-derived dynamics of virion-bound Envs. Unliganded SOSIP measurements were consistent with closed, neutralizing antibody-bound structures and shielding of non-neutralizing epitopes, demonstrating homogeneity at Env apex, increased flexibility near Env base, and no evidence for the intra-subunit flexibility near Env apex suggested by smFRET. CD4 binding increased inter-subunit distances and heterogeneity, consistent with rearrangements required for coreceptor binding. Results suggest similarities between SOSIPs and virion-bound Envs and demonstrate DEER’s relevance for immunogen design
AI ATAC 1: An Evaluation of Prominent Commercial Malware Detectors
This work presents an evaluation of six prominent commercial endpoint malware
detectors, a network malware detector, and a file-conviction algorithm from a
cyber technology vendor. The evaluation was administered as the first of the
Artificial Intelligence Applications to Autonomous Cybersecurity (AI ATAC)
prize challenges, funded by / completed in service of the US Navy. The
experiment employed 100K files (50/50% benign/malicious) with a stratified
distribution of file types, including ~1K zero-day program executables
(increasing experiment size two orders of magnitude over previous work). We
present an evaluation process of delivering a file to a fresh virtual machine
donning the detection technology, waiting 90s to allow static detection, then
executing the file and waiting another period for dynamic detection; this
allows greater fidelity in the observational data than previous experiments, in
particular, resource and time-to-detection statistics. To execute all 800K
trials (100K files 8 tools), a software framework is designed to
choreographed the experiment into a completely automated, time-synced, and
reproducible workflow with substantial parallelization. A cost-benefit model
was configured to integrate the tools' recall, precision, time to detection,
and resource requirements into a single comparable quantity by simulating costs
of use. This provides a ranking methodology for cyber competitions and a lens
through which to reason about the varied statistical viewpoints of the results.
These statistical and cost-model results provide insights on state of
commercial malware detection
Cooperação internacional em ciência, tecnologia e inovação: uma análise dos atos bilaterais entre Brasil e China.
TCC (graduação) - Universidade Federal de Santa Catarina. Centro Sócio-Econômico. Relações Internacionais.Este trabalho tem por objetivo geral analisar os atos bilaterais em ciência tecnologia e inovação entre Brasil e China, identificando o seu perfil, mudanças e similaridades entre o século XX e XXI e verificando possíveis fatores que poderiam influenciar a cooperação nessa área. Para cumprir com esse objetivo, realiza-se uma pesquisa exploratória, com natureza qualitativa e técnica de pesquisa bibliográfica e documental. A partir disso, faz-se uma revisão de literatura sobre cooperação internacional e as relações entre Brasil e China e sistematizamse todos os atos bilaterais em C,T&I entre Brasil e China publicados na plataforma de atos internacionais do Itamaraty, a “Concórdia”. As principais descobertas realizadas por este trabalho são: que o perfil dos atos bilaterais entre Brasil e China em ciência, tecnologia e inovação é simétrico; que se tem uma alta similaridade entre a cooperação bilateral sinobrasileira do século XX e XXI; que a área espacial representa uma constante como o setor de cooperação sino-brasileira em ciência, tecnologia e inovação, com o maior número de atos assinados em ambos os séculos; que visitas presidenciais podem representar um fator de influência na assinatura de atos de cooperação; e que a mutualidade de interesses entre Brasil e China e a reciprocidade de sua cooperação bilateral poderiam ser fatores que influenciam a sua cooperação em ciência, tecnologia e inovação
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